Special Weather Statement, NWS Huntsville, AL

Area Forecast Discussion
National Weather Service Huntsville AL
1254 PM CDT Mon Jul 26 2021

.UPDATE...
For 18Z TAFS.

&&

.NEAR TERM...(Rest of Today)
Issued at 1053 AM CDT Mon Jul 26 2021

Patchy dense fog that sharply reduced visibilities over portions of
NE Alabama (like Ft Payne and wind sheltered valleys) has dissipated
with daytime heating and mixing. Temperatures were rising through the
mid/upper 80s. This has reached convective temperatures, with CU/TCU
formation in progress. A more notable CU field extending from east
of Tupelo to Huntsville and Lynchburg has resulted in showers already
forming over parts of NW and north central Alabama.

Expect more showers and thunderstorms to form during the course of
the late morning continuing into the afternoon. Morning soundings
from OHX and BMX both have precip water amounts in the 2 inch range.
Current slow cell movement per our new convection and convection on-
going on the south side of Nashville, will bring chances of locally
heavy rain and a potential of flash flooding mainly this afternoon.

Have lowered high temperatures a degree or two given the formation of
clouds and showers. Afternoon heat indexes will still rise into the
100-104 degree range in areas unaffected by showers. Otherwise, the
overall forecast for the rest of the day appears to be on track.

.SHORT TERM...(Tonight through Wednesday)
Issued at 520 AM CDT Mon Jul 26 2021

Models indicate little change in the synoptic regime overnight, with
low probabilities for showers and thunderstorms expected to persist
for much of the night, given the number of outflow boundaries that
will likely be in the region. We have indicated a low chance POP for
the evening hours and reduced this to slight chance during the early
morning hours on Tuesday, when patchy fog may also occur in a few
locations.

During the period from Tuesday-Wednesday, the subtropical high
positioned across the central Rockies will begin to intensify and
shift east-southeastward into the central Plains. A stronger
northeasterly flow aloft will become established across the local
area, as an amplifying ridge attached to the high begins to build
southeastward, with the advection of drier air aloft and a general
increase in subsidence warranting a rapid decrease in POPs on Tuesday
night/Wednesday. However, before this occurs, we still anticipate
scattered-numerous showers and thunderstorms on Tuesday afternoon.
Although highs will be a few degrees cooler on Tuesday due to more
cloud cover during the morning, temps will soar back into the l-m 90s
on Wednesday, with a Heat Advisory possible for portions of the
CWFA.as several disturbance will track southeastward in this flow
regime and interact with a stalled frontal boundary.

.LONG TERM...(Wednesday night through Sunday)
Issued at 520 AM CDT Mon Jul 26 2021

Strong ridging aloft will remain the dominant feature of interest
from Wednesday night-Thursday night, with the hottest day of the
summer (thus far) expected on Thursday, when highs will reach the m-u
90s. Although some mixing of the boundary layer moisture will allow
for slightly lower dewpoints (u60s-l70s), predicted heat index values
are still several degrees above Heat Advisory criteria for most of
the forecast area. The subtropical ridge will slowly begin to break
down and shift southwestward beginning on Friday, as a longwave
trough amplifies across eastern Canada. It appears as if a slightly
more defined cold front will push southward into the region late
Friday afternoon, with a few showers and thunderstorms possible. As
the influence of the subtropical ridge diminishes this weekend,
deep- layer northwest flow will strengthen across the TN Valley,
which could result in a rather active period of convection, some of
which could be strong-severe based on a favorable combination of
shear and instability.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1254 PM CDT Mon Jul 26 2021

Strong daytime heating and a humid environment has resulted in the
formation of CU/TCU/CB across the area. A primary area of convection
extends from NE of KTUP, to NW of KMSL, near KGZS, drifting ESE
around 5 mph. Thus, scattered to numerous showers and thunderstorms
look likely this afternoon and early evening. A slow moving storm
impacting a terminal could produce erratic gusty winds, as well as
CIG/VSBY reductions, frequent lightning and torrential rainfall.
Shower activity should wind down with a loss of heating this evening.
Residual moisture, especially in/near locations that receive rainfall
could be impacted by fog in the overnight. With guidance in general
agreement, have followed suit and reduced VSBY at both sites into the
MVFR, with TEMPO IFR. Conditions should improve after sunrise, with
VFR weather expected by 14Z Tue morning.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&

NEAR TERM...RSB
SHORT TERM...70/DD
LONG TERM...70/DD
AVIATION...RSB

For more information please visit our website at
weather.gov/huntsville.

Hazardous Weather Outlook
National Weather Service Huntsville AL
640 AM CDT Mon Jul 26 2021

ALZ001>010-016-TNZ076-096-097-271130-
Lauderdale-Colbert-Franklin AL-Lawrence-Limestone-Madison-Morgan-
Marshall-Jackson-DeKalb-Cullman-Moore-Lincoln-Franklin TN-
640 AM CDT Mon Jul 26 2021

This Hazardous Weather Outlook is for north Alabama and portions of
southern middle Tennessee.

.DAY ONE...Today and Tonight...

Numerous thunderstorms are anticipated across the Tennessee Valley
today, with the greatest coverage occurring during the afternoon and
early evening hours. Although the coverage of thunderstorms will
diminish overnight, a few storms could occur through sunrise. Wind
gusts of 40 to 50 MPH and frequent cloud to ground lightning will be
possible with the strongest cells. Due to slow storm motions and high
rainfall rates, flash flooding will also be possible in localized
areas.

For locations in northwest and north central Alabama that do not
experience a cooling shower or storm today, dangerously high heat
index values in the 100-105 degree range are expected.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday...

Scattered to numerous thunderstorms are expected on Tuesday, with
only isolated storms anticipated south of the Tennessee River on
Wednesday. After a break in precipitation on Thursday, scattered
thunderstorms will return to the region from Friday through Sunday.

Dangerously high heat indices in the 100 to 105 degree range are
expected for most locations in the Tennessee Valley on Wednesday,
Thursday and Friday.

.SPOTTER CALL TO ACTION STATEMENT...

Activation of storm spotters and emergency management personnel is
not anticipated at this time.

70/DD

Special Weather Statement
National Weather Service Huntsville AL
128 PM CDT Mon Jul 26 2021

ALZ002-003-261900-
Franklin AL-Colbert AL-
128 PM CDT Mon Jul 26 2021

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN COLBERT AND NORTHERN
FRANKLIN COUNTIES UNTIL 200 PM CDT...

At 127 PM CDT, Doppler radar was tracking a strong thunderstorm near
Cherokee, or 9 miles northeast of Tishomingo State Park, moving
southeast at 5 mph.

Pea size hail and winds in excess of 30 mph will be possible with
this storm.

Locations impacted include...
Cherokee, Malone, Mynot, Mt Hester, Margerum, Maud, Allsboro and
Barton.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Strong gusty winds will be capable of knocking down small tree limbs
along with other small unsecured items. Seek safe shelter until this
storm has passed.

Very heavy rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 3462 8813 3472 8812 3479 8807 3473 8786
      3454 8803 3461 8814
TIME...MOT...LOC 1827Z 300DEG 6KT 3468 8804

25